1. The Field of the Invention
The present invention relates to a method for forming a multi-layered thin film and, more particularly, to a method and an apparatus for forming a multi-layered thin film using a photolysis chemical vapor deposition (PCVD) by which a thin film is deposited using light energy.
2. Description of the Related Art
A multi-layered thin film having a combination of different materials is widely used for photoelectron devices and magnetic cells as well as semiconductor devices because it has unique characteristics compared to a single layer thin film. In the semiconductor industry, a physical vapor deposition method and a chemical vapor deposition method are most widely used to form thin films. These methods are mostly used to form a single layer using one or two source gases. When forming a multi-layered thin film, various source gases can be alternatively supplied to form the multi-layered thin film. However, these methods suffer from drawbacks such as the lack of process stability or the difficulty in the configuration of various apparatuses.
Layer-by-layer deposition methods have been extensively studied as techniques for forming a multi-layered thin film. A single crystal compound having a desired composition and few defects may be formed by the layer-by-layer deposition techniques.
Molecular beam epitaxy (MBE) and cyclic CVD, which is an atomic layer deposition (ALD) method, or digital CVD are examples of such layer-by-layer deposition techniques. However, in the case of MBE, equipment is very expensive and productivity is low. Thus, the ALD method is getting the most attention among those layer-by-layer deposition methods.
In the ALD method, two different layers are sequentially stacked on a substrate by alternatingly supplying two different source gases into a deposition reactor, thereby forming a multi-layered thin film. Since this ALD method does not require a high vacuum state necessary for the above-described MBE, it has an advantage of increased deposition rate.
However, when a multi-layered thin film is formed by this conventional ALD method, a gas purge step using an inert gas is inevitably added between steps of forming each layer of the multi-layered thin film in order to remove an unwanted layer formed due to physical adsorption on a substrate.
Because of such additional purging steps in the conventional ALD, deposition efficiency is low and there have been difficulties in equipment maintenance because a purging valve has to be repeatedly opened and closed. Thus, the conventional ALD method has a limit in mass production.